Silane functional oligomer

Abstract

A silane functional oligomer for use in the formulation of coating compositions having good clarity which has at east one hydrolyzable silane group and which is the reaction product of; (i) a silane coupling agent having a hydrolyzable silane group and a secondary amine group, (ii) a polyisocyanate having more than one tertiary isocyanate group, and containing at least 6% by weight of NCO groups, and (iii) optionally, compound having single isocyanate reactive group.

We claim: 
     
       1. A silane functional oligomer which has at least one hydrolyzable silane group and which is the reaction product of; (i) a silane coupling agent having a hydrolyzable silane group and a secondary amine group,   (ii) a polyisocyanate having more than one tertiary isocyanate group, and containing at least 6% by weight of NCO groups, which is the reaction product of tetramethylxylene diisocyanate and trimethylol propane, and   (iii) optionally, a compound having a single isocyanate-reactive group.   
     
     
       2. An oligomer as claimed in claim 1 which has on average between 1 and 3 hydrolyzable silane groups. 
     
     
       3. An oligomer as claimed in claim 1 or claim 2 in which the silane coupling agent is of Formula (III); ##STR5## in which R I , R II  and R III  are independently C 1  to 6 alkyl, n is 1 to 6 and a is 1 to 3. 
     
     
       4. An oligomer as claimed in any one of claim 1 in which the polyisocyanate has an average of 2 or more tertiary isocyanate groups. 
     
     
       5. An oligomer as claimed in claim 1 in which the compound having a single isocyanate-reactive group is a monoalcohol. 
     
     
       6. A process for making an oligomer as claimed in claim 1 which comprises reacting together the silane coupling agent, the polyisocyanate and, optionally, the compound having a single isocyanate-reactive group. 
     
     
       7. A coating composition comprising an oligomer as claimed in claim 1 and a silane functional polymer. 
     
     
       8. A coating composition as claimed in claim 7 in which the polymer is an addition polymer. 
     
     
       9. A composition as claimed in claim 7 or claim 8 in which the components are present in amounts such that the ratio of the number of silane groups on the oligomer to the number of silane groups on the polymer is in the range 10:1 to 1:10. 
     
     
       10. A method of making a coating composition as claimed in claim 7 which comprised mixing an oligomer as claimed in claim 1 with a silane functional polymer. 
     
     
       11. A coating process which comprises applying a layer of a coating composition as claimed in claim 7 to a surface of a substrate and the causing or allowing the layer to cure. 
     
     
       12. A coated substrate obtained by the process of claim 11.